Detection of a nearby cased well, evaluating the distance from it, and its direction are important for steering with respect to a cased well or for collision avoidance. Steam assisted gravity drainage (SAGD) is such an application, where an injector well is drilled at a given distance parallel to a cased producer well. For collision avoidance applications, the objective is to detect the casings in order to avoid these wells. That is particularly useful for drilling new wells out of offshore platforms where the density of existing wells could be high.
A commonly used technique for evaluating formations surrounding an earth borehole is resistivity logging. A porous formation having a high resistivity generally indicates the presence of hydrocarbons, while a porous formation with low resistivity generally indicates water saturation, for example. Modern resistivity logging tools operate by transmitting a signal from a transmitter station and measuring the voltage of the received signal at a receiver station. These voltages are referred to as coupling voltages and are sensitive to the formation properties.
Such modern resistivity logging tools are already used in logging while drilling applications. Thus, ways to utilize resistivity logging tools to detect nearby cased wells would be particularly desirable.